Kennedy's Disease, also known as Spinal Bulbar Muscular Atrophy, bulbo-spinal atrophy, X-linked bulbospinal neuropathy (XBSN), or X-linked spinal muscular atrophy type 1 (SMAX1), is a neuromuscular degenerative disease affecting males who carry a mutation in the Androgen Receptor (AR) gene on the X chromosome. Kennedy's Disease is caused by expansion of a trinucleotide CAG repeat in exon 1 of the androgen receptor gene that encodes a polyglutamine tract in the androgen receptor protein.
There is a positive correlation between CAG repeat length and disease severity, and a negative correlation between repeat length and the age of disease onset. The number of CAG repeats in Kennedy's Disease patients varies, but can be in the range of about 36-62 repeats. Kennedy's Disease is characterized by the degeneration and loss of lower motor neurons in the brainstem and spinal cord, together with progressive weakness, atrophy and fasciculation of proximal limb and bulbar muscles combined with sensory impairment. Kennedy's Disease usually develops in middle adult life, but onset and severity of the disease can vary from adolescence to old age.
Currently there are no cures or treatments for Kennedy's Disease. Males suffering from Kennedy's Disease commonly end up in a wheelchair as a result of motor neuron degeneration and muscle wasting, and are subsequently at higher risk of developing other ailments.